The production of renewable fuels through water splitting via photocatalytic hydrogen production holds significant promise.Nonetheless,the sluggish kinetics of hydrogen evolution and the inadequate water adsorption on...The production of renewable fuels through water splitting via photocatalytic hydrogen production holds significant promise.Nonetheless,the sluggish kinetics of hydrogen evolution and the inadequate water adsorption on photocatalysts present notable challenges.In this study,we have devised a straightforward hydrothermal method to synthesize Bi_(2)O_(3)(BO)derived from metal‐organic frameworks(MOFs),loaded with flower-like ZnIn_(2)S_(4)(ZIS).This approach substantially enhances water adsorption and surface catalytic reactions,resulting in a remarkable enhancement of photocatalytic activity.By employing triethanolamine(TEOA)as a sacrificial agent,the hydrogen evolution rate achieved with 15%(mass fraction)ZIS loading on BO reached an impressive value of 1610μmol∙h^(−1)∙g^(−1),marking a 6.34-fold increase compared to that observed for bare BO.Furthermore,through density functional theory(DFT)and ab initio molecular dynamics(AIMD)calculations,we have identified the reactions occurring at the ZIS/BO S-scheme heterojunction interface,including the identification of active sites for water adsorption and catalytic reactions.This study provides valuable insights into the development of high-performance composite photocatalytic materials with tailored electronic properties and wettability.展开更多
Two-dimensional covalent organic frameworks(2D COFs)feature extendedπ-conjugation and ordered stacking sequence,showing great promise for high-performance photocatalysis.Periodic atomic frameworks of 2D COFs facilita...Two-dimensional covalent organic frameworks(2D COFs)feature extendedπ-conjugation and ordered stacking sequence,showing great promise for high-performance photocatalysis.Periodic atomic frameworks of 2D COFs facilitate the in-plane photogenerated charge transfer,but the precise ordered alignment is limited due to the non-covalentπ-stacking of COF layers,accordingly hindering out-of-plane transfer kinetics.Herein,we address a chiral induction method to construct a parallelly superimposed stacking chiral COF ultrathin shell on the support of SiO_(2) microsphere.Compared to the achiral COF analogues,the chiral COF shell with the parallel AA-stacking structure is more conducive to enhance the built-in electric field and accumulates photogenerated electrons for the rapid migration,thereby affording superior photocatalytic performance in hydrogen evolution from water splitting.Taking the simplest ketoenamine-linked chiral COF as a shell of SiO_(2) particle,the resulting composite exhibits an impressive hydrogen evolution rate of 107.1 mmol g^(-1)h^(-1)along with the apparent quantum efficiency of 14.31% at 475 nm.Furthermore,the composite photocatalysts could be fabricated into a film device,displaying a remarkable photocatalytic performance of 178.0 mmol m^(-2)h^(-1)for hydrogen evolution.Our work underpins the surface engineering of organic photocatalysts and illustrates the significance of COF stacking structures in regulating electronic properties.展开更多
Polyether ether ketone(PEEK)has good mechanical properties.However,its high viscosity when molten limits its use because it is hard to process.PEEK nanocomposites containing both carbon nanotubes(CNTs)and polyether im...Polyether ether ketone(PEEK)has good mechanical properties.However,its high viscosity when molten limits its use because it is hard to process.PEEK nanocomposites containing both carbon nanotubes(CNTs)and polyether imide(PEI)were pre-pared by a direct wet powder blending method using a vertical injection molding machine.The addition of an optimum amount of PEI lowered the viscosity of the molten PEEK by approximately 50%while producing an increase in the toughness of the nanocom-posites,whose strain to failure increased by 129%,and fracture energy increased by 97%.The uniformly dispersed CNT/PEI powder reduced the processing difficulty of PEEK nanocomposites without affecting the thermal resistance.This improvement of the strength and viscosity of PEEK facilitate its use in the preparation of thermoplastic composites.展开更多
The mixed grain structure and mechanical property anisotropy of AZ40 magnesium alloy bar with a diameter of 160 mm manufactured by "multi-direction forging(MDF) + extrusion + online cooling" technique were inves...The mixed grain structure and mechanical property anisotropy of AZ40 magnesium alloy bar with a diameter of 160 mm manufactured by "multi-direction forging(MDF) + extrusion + online cooling" technique were investigated by optical microscopy(OM), scanning electron microscopy(SEM), X-ray diffraction macro-texture measurement and room temperature(RT) tensile test. The results show that mixed grain structure is caused by the micro-segregation of Al in semi-continuous casting ingot. Homogenization of(380 °C, 8 h) +(410 °C, 12 h) cannot totally eliminate such micro-segregation. During MDF and extrusion, the dendrite interiors with 3%-4% Al(mass fraction) transform to fine grain zones, yet the dendrite edges with about 6% Al transform to coarse grain zones. XRD macro-textures of the outer, R/2 and center show typical fiber texture characteristics and the intensity of [0001]//Ra D orientation in the outer(11.245) is about twice as big as those in the R/2(6.026) and center(6.979). The as-extruded AZ40 magnesium alloy bar has high elongation(A) and moderate ultimate tensile strength(Rm) in both extrusion direction(ED) and radius direction(Ra D), i.e., A of 19%-25% and Rm of 256-264 MPa; however, yield strength(Rp0.2) shows anisotropy and heterogeneity, i.e., 103 MPa in Ra D, 137 MPa in ED-C(the center) and 161 MPa in ED-O(the outer), which are mainly caused by the texture.(155 °C, 7 h) +(170 °C, 24 h) aging has no influence on strength and elongation of AZ40 magnesium bar.展开更多
To meet the demands for large space and flexible compartmentation ofbuildings, laminated vierendeel trasses are adopted in high-position transfer story structures.First the bearing characteristics are analyzed, in whi...To meet the demands for large space and flexible compartmentation ofbuildings, laminated vierendeel trasses are adopted in high-position transfer story structures.First the bearing characteristics are analyzed, in which reasonable stiffness ratio of the upperchord, middle chord, and lower chord is derived. Then combined with an actual engineering model (1:8similar ratio), the static loading and pseudo-dynamic tests of two models for laminated vierendeeltrass used in transfer story structures are conducted, in which one model adopts reinforcedconcrete, and the other adopts prestressed concrete and shape steel concrete. Seismic behaviors areanalyzed, including inter-story displacement, base shear-displacement skeleton curves, andequivalent viscosity-damping curves. A program is programmed to carry out the elasto-plastic dynamicanalysis, and displacement time-history curves of the two models are derived. The test and analysisresults show that the laminated vierendeel trass with prestressed concrete and shape steel concretehas excellent seismic behaviors. It can solve the disadvantages of laminated vierendeel trussesused in transfer story structures. Finally, some design suggestions are put forward, which can bereferenced by similar engineering.展开更多
The analogy between the wave equation of liquid and the Navier equations of structural elasticity is examined in detail. By introducing appropriate parameters, the structural counterpart of the liquid sloshing model c...The analogy between the wave equation of liquid and the Navier equations of structural elasticity is examined in detail. By introducing appropriate parameters, the structural counterpart of the liquid sloshing model can be easily built. Therefore, the dynamic analysis of liquid sloshing can be reduced to that of structural elasticity, and the existing FEM structural analysis computer programs can be applied to liquid sloshing analysis without any modification. The present method also reveals the internal relationship between liquid sloshing and structural vibration. The effectiveness and reliability of the method is illustrated by the numerical example.展开更多
Let X be a metric space with an ordering structure,A: X→X is a operator and x≤Ax for any x∈X. In this paper we prove a new fixed point theorem, which generalizes famous caristi fixed point theorem.
High-speed bogie frame is a key mechanical component in a train system. The reliability analysis of the bogie is necessary to the safety of high-speed train. Reliability analysis of a bogie frame was considered. The e...High-speed bogie frame is a key mechanical component in a train system. The reliability analysis of the bogie is necessary to the safety of high-speed train. Reliability analysis of a bogie frame was considered. The equivalent load method was employed to account for random repeated loads in structural reliability analysis. Degradation of material strength was regarded as a Gamma process. The probabilistic perturbation method was, then, employed for response moment computation. Example of a high-speed train bogie structure under time-variant load was employed for reliability and sensitivity analyses. Monte-Carlo simulation verifies the accuracy and efficiency of the proposed method in time-variant reliability analysis. The analysis results show that the reliability calculation considering the strength degradation and repeated load is closer to the practicality than the method of considering reliability calculation only. Its decreasing velocity is faster than the traditional reliability. The reliability sensitivity value changes over time. The analysis results provide a variation trend of reliability and sensitivity to design and usage of bogie frame.展开更多
The effect of microstructure evolution on the tensile properties of 2050 Al-Li alloy thick plate aged at 150 ℃ with 80 mm in thickness(t) was studied from a microstructural perspective. Scanning electron microscope, ...The effect of microstructure evolution on the tensile properties of 2050 Al-Li alloy thick plate aged at 150 ℃ with 80 mm in thickness(t) was studied from a microstructural perspective. Scanning electron microscope, optical microscope, transmission electron microscope and X-ray diffractometer were used to explore the surface(t/6), interlayer(t/3) and center(t/2) thickness layer of this alloy. Results show that the secondary phases on grain boundaries, precipitates and textures vary depending on the thickness location. The precipitation strengthening has a stronger influence on the alloy along the rolling direction than the transverse direction from the under-aged to the peak-aging condition;however, its effect on the anisotropy is insignificant. The higher Taylor factor(M) value caused by stronger β fiber rolling textures and the intergranular phases is the main reason that leads to the highest strength at the t/2 position along the rolling direction. The M-value has a limited change at different thickness layers along the transverse direction, which causes the same tensile strength.展开更多
A special form of the Stewart platform is presented in which the top platform and base platform are similar and corresponding vertices are connected by six prismatic joints.A closed-from solution for the forward displ...A special form of the Stewart platform is presented in which the top platform and base platform are similar and corresponding vertices are connected by six prismatic joints.A closed-from solution for the forward displacement analysis of this mechanism is developed.When the six vertices of the top platform are in a quadratic curve,this mechanism becomes singular.This new theoretical result is confirmed with a numerical example.展开更多
The microstructure evolution and strengthening mechanisms of Mg-10Gd-1Er-1Zn-0.6Zr(wt.%) alloy were focused in the view of the size parameters and volume fraction(fp) of dual phases(long period stacking ordered(LPSO) ...The microstructure evolution and strengthening mechanisms of Mg-10Gd-1Er-1Zn-0.6Zr(wt.%) alloy were focused in the view of the size parameters and volume fraction(fp) of dual phases(long period stacking ordered(LPSO) structures and β’ precipitates).Results show that two types of LPSO phases with different morphologies formed,and the morphology and size of both LPSO phases varied with the solution conditions.However,the volume fraction decreased monotonously with increasing solution temperature,which in turn raised the volume fraction of β’ phase during aging.The alloy exhibited an ultimate tensile strength of 352 MPa,a yield strength of 271 MPa,and an elongation of 3.5% after solution treatment at 500℃ for 12 h and aging at 200℃ for 114 h.In contrast to the LPSO phase,the β’ phase seems to play a more important role in enhancing the yield strength,and consequently,a decreased fLPSO/fβ’,ratio results in an increased yield strength.展开更多
For the requirement of safe and stable operation,the combined sealing structure was used for reciprocating motion in the deep sea high-pressure environment,and the effects of different seawater depths and shaft moveme...For the requirement of safe and stable operation,the combined sealing structure was used for reciprocating motion in the deep sea high-pressure environment,and the effects of different seawater depths and shaft movement speed on the sealing performance of the combined sealing structure were studied.The change rule of the sealing performance of the combined sealing structure of reciprocating motion under different working conditions is proved.The study shows that in the combined sealing structure of reciprocating movement,the Von Mises stress and the contact stress of the O-ring varies with the direction of the shaft movement.The Von Mises stress and contact stress of the O-ring,the Von Mises stress and the contact stress on each sealing lip of the slip ring gradually increase with the increasing of seawater depths.At the same time,the Von Mises stress of the O-ring which in the process of the shaft upward movement is greater than the shaft downward movement,making the shaft upward movement more likely to cause the O-ring relaxation and fatigue.The shaft movement speed has no significant influence on the Von Mises stress and contact stress of the O-ring.The research results provide theoretical guidance and technical support for the selection and optimization of the geometrical parameters of the combined sealing structure in the deep-sea high-pressure environment.展开更多
A commercial AA7108 aluminium alloy subjected to different quenching procedures from the solid solution temperature of 480 ℃ was considered. Both continuously cooling and quenching to intermediate temperatures (400,...A commercial AA7108 aluminium alloy subjected to different quenching procedures from the solid solution temperature of 480 ℃ was considered. Both continuously cooling and quenching to intermediate temperatures (400, 300 and 200 ℃) followed by different holding times were applied. All the materials were subsequently subjected to the same industrial two-step artificial ageing procedure to obtain a maximum strength (T6). Tensile testing of the different quenched materials in the T6 temper reveals a large deviation in strength dependent on the cooling/holding time, compared with the reference sample. A collection of the different quenched materials was chosen for further investigation of the precipitate structure by transmission electron microscopy (TEM) to explain the differences in mechanical properties.展开更多
The high precision assemblies with considerable radial interference should be accompanied by heating and cooling processes.However,the mechanical properties of metals are greatly affected by thermal operations.So,for ...The high precision assemblies with considerable radial interference should be accompanied by heating and cooling processes.However,the mechanical properties of metals are greatly affected by thermal operations.So,for evaluating the stress distribution and distortion of teeth profiles in a gear/shaft assembly,a transient thermal analysis is necessary for finding the change in mechanical properties.The friction on the contact surface is another important parameter in interaction of the gear with the shaft.Evaluating the gear stress and deformation fields for several modes of heat transfer and friction coefficients showed that the maximum radial or tangential stresses on contact surface of the joint may have more than 8%increase by increasing friction coefficient;while the intensity of heat transfer at cooling stage has lower effect on stress distribution.展开更多
The exploration of stable and highly efficient alkaline hydrogen evolution reaction(HER)electrocatalysts is imperative for alkaline water splitting.Herein,Se-doped NiCoP with hierarchical nanoarray structures directly...The exploration of stable and highly efficient alkaline hydrogen evolution reaction(HER)electrocatalysts is imperative for alkaline water splitting.Herein,Se-doped NiCoP with hierarchical nanoarray structures directly grown on carbon cloth(Se-NiCoP/CC)was prepared by hydrothermal reaction and phosphorization/selenization process.The experimental results reveal that Se doping could increase the electrochemical active sites and alter the electronic structure of NiCoP.The optimized Se-NiCoP/CC electrode exhibits outstanding HER activity in alkaline electrolyte,which only needs a low overpotential of 79 mV at the current density of 10 mA/cm^(2).When serving as anode and cathode electrode simultaneously,the Se-NiCoP/CC electrodes achieve current density of 50 mA/cm^(2) at a low voltage of only 1.62 V.This work provides a feasible way to rationally design high active HER electrocatalysts.展开更多
The ultrasonic motor (USM) possesses heavy nonlinearities which vary with driving conditions and load-dependent characteristics such as the dead-zone. In this paper, an identification method for the rotary travelling-...The ultrasonic motor (USM) possesses heavy nonlinearities which vary with driving conditions and load-dependent characteristics such as the dead-zone. In this paper, an identification method for the rotary travelling-wave type ultrasonic motor (RTWUSM) with dead-zone is proposed based on a modified Hammerstein model structure. The driving voltage contributing effect on the nonlinearities of the RTWUSM was transformed to the change of dynamic parameters against the driving voltage. The dead-zone of the RTWUSM is identified based upon the above transformation. Experiment results showed good agreement be- tween the output of the proposed model and actual measured output.展开更多
The effects of different solution methods on microstructure, mechanical properties and precipitation behavior of Al-Mg-Si alloy were investigated by scanning electron microscope, transmission electron microscope, tens...The effects of different solution methods on microstructure, mechanical properties and precipitation behavior of Al-Mg-Si alloy were investigated by scanning electron microscope, transmission electron microscope, tensile test, and differential scanning calorimetry. The results revealed that the recrystallized grains of the alloy after the solution treatment with hot air became smaller and more uniform, compared with solution treatment with electrical resistance. The texture of the alloy after two solution treatment methods was different. More rotated cube components were formed through solution treatment with electrical resistance, which was better for improving the drawability of the alloy. The strength of the alloy under the solution treatment with hot air was higher before stamping, because of the small uniform grains and many clusters in the matrix. The alloy solution treated with hot air also possessed good bake hardenability, because the transformation occurred on more clusters in the matrix.展开更多
The cable-strut structural system is statically and kinematically indeterminate. The initial pre-stress is a key factor for determining the shape and load carrying capacity. A new numerical algorithm is presented here...The cable-strut structural system is statically and kinematically indeterminate. The initial pre-stress is a key factor for determining the shape and load carrying capacity. A new numerical algorithm is presented herein for the initial pre-stress finding procedure of complete cable-strut assembly. This method is based on the linear adjustment theory and does not take into account the material behavior. By using this method,the initial pre-stress of the multi self-stress modes can be found easily and the cal-culation process is simplified and efficient also. Finally,the initial pre-stress and structural performances of a particular Levy cable dome are analyzed comprehensively. The algorithm has proven to be efficient and correct,and the numerical results are valuable for practical design of Levy cable dome.展开更多
文摘The production of renewable fuels through water splitting via photocatalytic hydrogen production holds significant promise.Nonetheless,the sluggish kinetics of hydrogen evolution and the inadequate water adsorption on photocatalysts present notable challenges.In this study,we have devised a straightforward hydrothermal method to synthesize Bi_(2)O_(3)(BO)derived from metal‐organic frameworks(MOFs),loaded with flower-like ZnIn_(2)S_(4)(ZIS).This approach substantially enhances water adsorption and surface catalytic reactions,resulting in a remarkable enhancement of photocatalytic activity.By employing triethanolamine(TEOA)as a sacrificial agent,the hydrogen evolution rate achieved with 15%(mass fraction)ZIS loading on BO reached an impressive value of 1610μmol∙h^(−1)∙g^(−1),marking a 6.34-fold increase compared to that observed for bare BO.Furthermore,through density functional theory(DFT)and ab initio molecular dynamics(AIMD)calculations,we have identified the reactions occurring at the ZIS/BO S-scheme heterojunction interface,including the identification of active sites for water adsorption and catalytic reactions.This study provides valuable insights into the development of high-performance composite photocatalytic materials with tailored electronic properties and wettability.
文摘Two-dimensional covalent organic frameworks(2D COFs)feature extendedπ-conjugation and ordered stacking sequence,showing great promise for high-performance photocatalysis.Periodic atomic frameworks of 2D COFs facilitate the in-plane photogenerated charge transfer,but the precise ordered alignment is limited due to the non-covalentπ-stacking of COF layers,accordingly hindering out-of-plane transfer kinetics.Herein,we address a chiral induction method to construct a parallelly superimposed stacking chiral COF ultrathin shell on the support of SiO_(2) microsphere.Compared to the achiral COF analogues,the chiral COF shell with the parallel AA-stacking structure is more conducive to enhance the built-in electric field and accumulates photogenerated electrons for the rapid migration,thereby affording superior photocatalytic performance in hydrogen evolution from water splitting.Taking the simplest ketoenamine-linked chiral COF as a shell of SiO_(2) particle,the resulting composite exhibits an impressive hydrogen evolution rate of 107.1 mmol g^(-1)h^(-1)along with the apparent quantum efficiency of 14.31% at 475 nm.Furthermore,the composite photocatalysts could be fabricated into a film device,displaying a remarkable photocatalytic performance of 178.0 mmol m^(-2)h^(-1)for hydrogen evolution.Our work underpins the surface engineering of organic photocatalysts and illustrates the significance of COF stacking structures in regulating electronic properties.
文摘Polyether ether ketone(PEEK)has good mechanical properties.However,its high viscosity when molten limits its use because it is hard to process.PEEK nanocomposites containing both carbon nanotubes(CNTs)and polyether imide(PEI)were pre-pared by a direct wet powder blending method using a vertical injection molding machine.The addition of an optimum amount of PEI lowered the viscosity of the molten PEEK by approximately 50%while producing an increase in the toughness of the nanocom-posites,whose strain to failure increased by 129%,and fracture energy increased by 97%.The uniformly dispersed CNT/PEI powder reduced the processing difficulty of PEEK nanocomposites without affecting the thermal resistance.This improvement of the strength and viscosity of PEEK facilitate its use in the preparation of thermoplastic composites.
基金Project(2013CB632202)supported by the National Basic Research Program of China
文摘The mixed grain structure and mechanical property anisotropy of AZ40 magnesium alloy bar with a diameter of 160 mm manufactured by "multi-direction forging(MDF) + extrusion + online cooling" technique were investigated by optical microscopy(OM), scanning electron microscopy(SEM), X-ray diffraction macro-texture measurement and room temperature(RT) tensile test. The results show that mixed grain structure is caused by the micro-segregation of Al in semi-continuous casting ingot. Homogenization of(380 °C, 8 h) +(410 °C, 12 h) cannot totally eliminate such micro-segregation. During MDF and extrusion, the dendrite interiors with 3%-4% Al(mass fraction) transform to fine grain zones, yet the dendrite edges with about 6% Al transform to coarse grain zones. XRD macro-textures of the outer, R/2 and center show typical fiber texture characteristics and the intensity of [0001]//Ra D orientation in the outer(11.245) is about twice as big as those in the R/2(6.026) and center(6.979). The as-extruded AZ40 magnesium alloy bar has high elongation(A) and moderate ultimate tensile strength(Rm) in both extrusion direction(ED) and radius direction(Ra D), i.e., A of 19%-25% and Rm of 256-264 MPa; however, yield strength(Rp0.2) shows anisotropy and heterogeneity, i.e., 103 MPa in Ra D, 137 MPa in ED-C(the center) and 161 MPa in ED-O(the outer), which are mainly caused by the texture.(155 °C, 7 h) +(170 °C, 24 h) aging has no influence on strength and elongation of AZ40 magnesium bar.
文摘To meet the demands for large space and flexible compartmentation ofbuildings, laminated vierendeel trasses are adopted in high-position transfer story structures.First the bearing characteristics are analyzed, in which reasonable stiffness ratio of the upperchord, middle chord, and lower chord is derived. Then combined with an actual engineering model (1:8similar ratio), the static loading and pseudo-dynamic tests of two models for laminated vierendeeltrass used in transfer story structures are conducted, in which one model adopts reinforcedconcrete, and the other adopts prestressed concrete and shape steel concrete. Seismic behaviors areanalyzed, including inter-story displacement, base shear-displacement skeleton curves, andequivalent viscosity-damping curves. A program is programmed to carry out the elasto-plastic dynamicanalysis, and displacement time-history curves of the two models are derived. The test and analysisresults show that the laminated vierendeel trass with prestressed concrete and shape steel concretehas excellent seismic behaviors. It can solve the disadvantages of laminated vierendeel trussesused in transfer story structures. Finally, some design suggestions are put forward, which can bereferenced by similar engineering.
文摘The analogy between the wave equation of liquid and the Navier equations of structural elasticity is examined in detail. By introducing appropriate parameters, the structural counterpart of the liquid sloshing model can be easily built. Therefore, the dynamic analysis of liquid sloshing can be reduced to that of structural elasticity, and the existing FEM structural analysis computer programs can be applied to liquid sloshing analysis without any modification. The present method also reveals the internal relationship between liquid sloshing and structural vibration. The effectiveness and reliability of the method is illustrated by the numerical example.
文摘Let X be a metric space with an ordering structure,A: X→X is a operator and x≤Ax for any x∈X. In this paper we prove a new fixed point theorem, which generalizes famous caristi fixed point theorem.
基金Projects(51135003,U1234208)supported by the National Natural Science Foundation of ChinaProject(IRT0816)supported by Program for Changjiang Scholars and Innovative Research Team in University of ChinaProject(N110603001)supported by the Fundamental Research Funds for the Central Universities of China
文摘High-speed bogie frame is a key mechanical component in a train system. The reliability analysis of the bogie is necessary to the safety of high-speed train. Reliability analysis of a bogie frame was considered. The equivalent load method was employed to account for random repeated loads in structural reliability analysis. Degradation of material strength was regarded as a Gamma process. The probabilistic perturbation method was, then, employed for response moment computation. Example of a high-speed train bogie structure under time-variant load was employed for reliability and sensitivity analyses. Monte-Carlo simulation verifies the accuracy and efficiency of the proposed method in time-variant reliability analysis. The analysis results show that the reliability calculation considering the strength degradation and repeated load is closer to the practicality than the method of considering reliability calculation only. Its decreasing velocity is faster than the traditional reliability. The reliability sensitivity value changes over time. The analysis results provide a variation trend of reliability and sensitivity to design and usage of bogie frame.
基金the National Natural Science Foundation of China(No.51961034)the Key Research and Development Program of Ningxia(No.2018BEB04037),China.
文摘The effect of microstructure evolution on the tensile properties of 2050 Al-Li alloy thick plate aged at 150 ℃ with 80 mm in thickness(t) was studied from a microstructural perspective. Scanning electron microscope, optical microscope, transmission electron microscope and X-ray diffractometer were used to explore the surface(t/6), interlayer(t/3) and center(t/2) thickness layer of this alloy. Results show that the secondary phases on grain boundaries, precipitates and textures vary depending on the thickness location. The precipitation strengthening has a stronger influence on the alloy along the rolling direction than the transverse direction from the under-aged to the peak-aging condition;however, its effect on the anisotropy is insignificant. The higher Taylor factor(M) value caused by stronger β fiber rolling textures and the intergranular phases is the main reason that leads to the highest strength at the t/2 position along the rolling direction. The M-value has a limited change at different thickness layers along the transverse direction, which causes the same tensile strength.
文摘A special form of the Stewart platform is presented in which the top platform and base platform are similar and corresponding vertices are connected by six prismatic joints.A closed-from solution for the forward displacement analysis of this mechanism is developed.When the six vertices of the top platform are in a quadratic curve,this mechanism becomes singular.This new theoretical result is confirmed with a numerical example.
基金Project(2016YFB0301101)supported by the National Key Research and Development Program of ChinaProject(Z161100002116033)supported by Beijing Municipal Science and Technology Commission,China+1 种基金Project(KZ201810005005)supported by Key Science and Technology Program of Beijing Municipal Commission of Education,ChinaProject(2172013)supported by Beijing Natural Science Foundation,China
文摘The microstructure evolution and strengthening mechanisms of Mg-10Gd-1Er-1Zn-0.6Zr(wt.%) alloy were focused in the view of the size parameters and volume fraction(fp) of dual phases(long period stacking ordered(LPSO) structures and β’ precipitates).Results show that two types of LPSO phases with different morphologies formed,and the morphology and size of both LPSO phases varied with the solution conditions.However,the volume fraction decreased monotonously with increasing solution temperature,which in turn raised the volume fraction of β’ phase during aging.The alloy exhibited an ultimate tensile strength of 352 MPa,a yield strength of 271 MPa,and an elongation of 3.5% after solution treatment at 500℃ for 12 h and aging at 200℃ for 114 h.In contrast to the LPSO phase,the β’ phase seems to play a more important role in enhancing the yield strength,and consequently,a decreased fLPSO/fβ’,ratio results in an increased yield strength.
基金supported by the National Natural Science Foundation of China (Grant No.51705145, 51779092)the National Key Research and Development Program of China (Grant No.2016YFC0300502 and No.2017YFC0307501)+1 种基金Natural Science Foundation of Hunan Province of China (Grant No.2019JJ50182)Research Foundation of Education Bureau of Hunan Province (Grant No.18B205)
文摘For the requirement of safe and stable operation,the combined sealing structure was used for reciprocating motion in the deep sea high-pressure environment,and the effects of different seawater depths and shaft movement speed on the sealing performance of the combined sealing structure were studied.The change rule of the sealing performance of the combined sealing structure of reciprocating motion under different working conditions is proved.The study shows that in the combined sealing structure of reciprocating movement,the Von Mises stress and the contact stress of the O-ring varies with the direction of the shaft movement.The Von Mises stress and contact stress of the O-ring,the Von Mises stress and the contact stress on each sealing lip of the slip ring gradually increase with the increasing of seawater depths.At the same time,the Von Mises stress of the O-ring which in the process of the shaft upward movement is greater than the shaft downward movement,making the shaft upward movement more likely to cause the O-ring relaxation and fatigue.The shaft movement speed has no significant influence on the Von Mises stress and contact stress of the O-ring.The research results provide theoretical guidance and technical support for the selection and optimization of the geometrical parameters of the combined sealing structure in the deep-sea high-pressure environment.
文摘A commercial AA7108 aluminium alloy subjected to different quenching procedures from the solid solution temperature of 480 ℃ was considered. Both continuously cooling and quenching to intermediate temperatures (400, 300 and 200 ℃) followed by different holding times were applied. All the materials were subsequently subjected to the same industrial two-step artificial ageing procedure to obtain a maximum strength (T6). Tensile testing of the different quenched materials in the T6 temper reveals a large deviation in strength dependent on the cooling/holding time, compared with the reference sample. A collection of the different quenched materials was chosen for further investigation of the precipitate structure by transmission electron microscopy (TEM) to explain the differences in mechanical properties.
文摘The high precision assemblies with considerable radial interference should be accompanied by heating and cooling processes.However,the mechanical properties of metals are greatly affected by thermal operations.So,for evaluating the stress distribution and distortion of teeth profiles in a gear/shaft assembly,a transient thermal analysis is necessary for finding the change in mechanical properties.The friction on the contact surface is another important parameter in interaction of the gear with the shaft.Evaluating the gear stress and deformation fields for several modes of heat transfer and friction coefficients showed that the maximum radial or tangential stresses on contact surface of the joint may have more than 8%increase by increasing friction coefficient;while the intensity of heat transfer at cooling stage has lower effect on stress distribution.
基金Projects(51772086,51872087,51971089)supported by the National Natural Science Foundation of ChinaProject(2018TP1037-202102)supported by Open Fund of Hunan Provincial Key Laboratory of Advanced Materials for New Energy Storage and Conversion,China+1 种基金Project supported by Student National SIT Innovation Program,ChinaProject(2020CB1007)supported by Hunan Joint International Laboratory of Advanced Materials and Technology for Clean Energy,China。
文摘The exploration of stable and highly efficient alkaline hydrogen evolution reaction(HER)electrocatalysts is imperative for alkaline water splitting.Herein,Se-doped NiCoP with hierarchical nanoarray structures directly grown on carbon cloth(Se-NiCoP/CC)was prepared by hydrothermal reaction and phosphorization/selenization process.The experimental results reveal that Se doping could increase the electrochemical active sites and alter the electronic structure of NiCoP.The optimized Se-NiCoP/CC electrode exhibits outstanding HER activity in alkaline electrolyte,which only needs a low overpotential of 79 mV at the current density of 10 mA/cm^(2).When serving as anode and cathode electrode simultaneously,the Se-NiCoP/CC electrodes achieve current density of 50 mA/cm^(2) at a low voltage of only 1.62 V.This work provides a feasible way to rationally design high active HER electrocatalysts.
基金Project supported by the National Natural Science Foundation of China (No. 60572055)the Natural Science Foundation of Guangxi Province (No. 0339068), China
文摘The ultrasonic motor (USM) possesses heavy nonlinearities which vary with driving conditions and load-dependent characteristics such as the dead-zone. In this paper, an identification method for the rotary travelling-wave type ultrasonic motor (RTWUSM) with dead-zone is proposed based on a modified Hammerstein model structure. The driving voltage contributing effect on the nonlinearities of the RTWUSM was transformed to the change of dynamic parameters against the driving voltage. The dead-zone of the RTWUSM is identified based upon the above transformation. Experiment results showed good agreement be- tween the output of the proposed model and actual measured output.
基金Project(2016YFB0300605)supported by the National Key Research and Development Program of ChinaProject(51234002)supported by the National Natural Science Foundation of China+1 种基金Project(L2013113)supported by the Liaoning Province Science and Technology,ChinaProject(N140703002)supported by the Fundamental Research Funds for the Central Universities,China
文摘The effects of different solution methods on microstructure, mechanical properties and precipitation behavior of Al-Mg-Si alloy were investigated by scanning electron microscope, transmission electron microscope, tensile test, and differential scanning calorimetry. The results revealed that the recrystallized grains of the alloy after the solution treatment with hot air became smaller and more uniform, compared with solution treatment with electrical resistance. The texture of the alloy after two solution treatment methods was different. More rotated cube components were formed through solution treatment with electrical resistance, which was better for improving the drawability of the alloy. The strength of the alloy under the solution treatment with hot air was higher before stamping, because of the small uniform grains and many clusters in the matrix. The alloy solution treated with hot air also possessed good bake hardenability, because the transformation occurred on more clusters in the matrix.
基金Project (No.863-705-210) supported by the Hi-Tech Research and Development Program (863) of China
文摘The cable-strut structural system is statically and kinematically indeterminate. The initial pre-stress is a key factor for determining the shape and load carrying capacity. A new numerical algorithm is presented herein for the initial pre-stress finding procedure of complete cable-strut assembly. This method is based on the linear adjustment theory and does not take into account the material behavior. By using this method,the initial pre-stress of the multi self-stress modes can be found easily and the cal-culation process is simplified and efficient also. Finally,the initial pre-stress and structural performances of a particular Levy cable dome are analyzed comprehensively. The algorithm has proven to be efficient and correct,and the numerical results are valuable for practical design of Levy cable dome.